Tools:
Ballpoint pen
A highlighter with suitable cap
Ruler
You probably need some cutting device
for the plastic card and lollipop stick etc but you'll figure that out later on.

So the method I've used to texture the tower is rather simple. You take the cap that preferably is somewhat brick shaped and push it in to the styrofoam then you fill in the imprint so it becomes more defined and permanent, it's not the inc you want. You want to break the surface layer of the styrofoam and widen the imprint that the dull cap probably won't manage.

Then do this to the entire tower.

I got a bit carried away an forgot both to take pictures of the inside and before I painted it. I'll try to make an sketch how the inside looks.

So the inside of the two blocks is hollowed out in triangular chunks overlapping the other side making the dice fall back and forth. Then I glued them together with some white glue and some toothpicks added like pinning. Put it in between pressure for a good long drying. Then grabbed just any kind of acrylic paint. One black and one white mixed a dark grey and then just added a bit more white for each layer.

Result:

The ugly hole was in the styrofoam from the begging and so deep I couldn't fix it but will cover it with a little shed.

The output will ad a wooden door.

The input will add an wooden platform so it can have troops act as a watchtower.

The base for the platform will add a a removable wall/boarder that goes around the platform. and the door for the hole where the dice comes out. with working hinges.

Leans a bit forward but that gets corrected by the base.

From above.

Failed attempt to stain the door. The superglue prevented the diluted paint to be absorbed. But you can see the added bolts/nails. I cut the blunt tip of some needles (not the kind with eyes). Then took my scalpel/ exacto knife put the point in and rotated so it carved out a little "dent" where the needle head fits perfectly.